title: Halotropism is a response of plant roots to avoid a saline environment.
abstract: Tropisms represent fascinating examples of how plants respond to environmental signals by adapting their growth and development. Here, a novel tropism is reported, halotropism, allowing plant seedlings to reduce their exposure to salinity by circumventing a saline environment. In response to a salt gradient, Arabidopsis, tomato, and sorghum roots were found to actively prioritize growth away from salinity above following the gravity axis. Directionality of this response is established by an active redistribution of the plant hormone auxin in the root tip, which is mediated by the PIN-FORMED 2 (PIN2) auxin efflux carrier. We show that salt-induced phospholipase D activity stimulates clathrin-mediated endocytosis of PIN2 at the side of the root facing the higher salt concentration. The intracellular relocalization of PIN2 allows for auxin redistribution and for the directional bending of the root away from the higher salt concentration. Our results thus identify a cellular pathway essential for the integration of environmental cues with auxin-regulated root growth that likely plays a key role in plant adaptative responses to salt stress.
authors.affiliation: Section of Plant Physiology, Swammerdam Institute for Life Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, the Netherlands.
authors.forename: Carlos S
authors.initials: CS
authors.lastname: Galvan-Ampudia
authors.forename: Magdalena M
authors.initials: MM
authors.lastname: Julkowska
authors.forename: Essam
authors.initials: E
authors.lastname: Darwish
authors.forename: Jacinto
authors.initials: J
authors.lastname: Gandullo
authors.forename: Ruud A
authors.initials: RA
authors.lastname: Korver
authors.forename: Geraldine
authors.initials: G
authors.lastname: Brunoud
authors.forename: Michel A
authors.initials: MA
authors.lastname: Haring
authors.forename: Teun
authors.initials: T
authors.lastname: Munnik
authors.forename: Teva
authors.initials: T
authors.lastname: Vernoux
authors.forename: Christa
authors.initials: C
authors.lastname: Testerink
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002966:Clathrin / Q000378:metabolism; D004705:Endocytosis; D007210:Indoleacetic Acids / Q000378:metabolism; D018551:Solanum lycopersicum / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D018519:Meristem / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018613:Microscopy, Confocal; D010739:Phospholipase D / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology*; D045868:Sorghum / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D018523:Tropism
chemical_list: D029681:Arabidopsis Proteins; D002966:Clathrin; D007210:Indoleacetic Acids; D010739:Phospholipase D; D010940:Plant Proteins; D012965:Sodium Chloride; C117013:AT5G57090 protein, Arabidopsis